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Who Generally Has the Higher IQ? Older Siblings or Younger Siblings?

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Firstborns really do have an advantage, a new U.K. study suggests. Research out of Edinburgh University finds that there's a measurable IQ difference between firstborns and their siblings, and it shows up as early as age 1, reports the BBC.

The reason? Parents tend to spend more time with their first children on games and tasks that develop thinking skills, such as reading and playing musical instruments, say the researchers. As later kids come along, parents get more strapped for time.

"It doesn't mean firstborns get more love — that stays the same," says researcher Ana Nuevo-Chiquero, per the Edinburgh News. "But they get more attention — especially in those important formative years."

The researchers examined data on 5,000 kids from pre-birth to age 14 in the U.S. Children of the National Longitudinal Survey of Youth, and correlated that with parental behavior. The kids were assessed every two years on a variety of skills, with firstborns generally outperforming siblings starting at 12 months. The edge increased slightly with age, and the scientists say that meshes with studies suggesting that firstborns end up in better-paying jobs as adults.

Not only did parents spend less time with their subsequent kids, but the mothers even took higher risks during pregnancy, like smoking, they report in the Journal of Human Resources.

(In related news, birth order may even influence weight.)